This invention relates to a filter element for a transcatheter embolic protection device.
The invention is particularly concerned with filter elements for transcatheter embolic protection devices of the type described in our WO-A-9923976. One type of such embolic filter comprises a filter body mounted on an associated collapsible support frame which can be collapsed against the guide wire by means of a catheter for deployment of the filter through a patient""s vascular system. Upon retraction of the catheter the support frame and filter body expand outwardly from the guidewire across a blood vessel within which the filter is positioned to filter blood flowing through the blood vessel.
A practical problem that arises with filter elements of such embolic protection devices is that they should be able to accommodate blood vessels of different diameter as it would be impractical to manufacture a large range of filters each of different size to accommodate all possible diameters of blood vessel. To provide flexibility and accommodate a range of vessel sizes with a given size of filter a relatively soft and elastic filter body material can be used. It is, however, important that the filter when deployed maintains its shape during use and to prevent distortion or collapsing of the filter body in use. Because of this and also the need for adequate strength in the body material, the walls of the filter body tend to be relatively thick. This presents a problem in that the filter then has relatively large crossing profile when in the collapsed delivery position, which is undesirable.
The present invention is directed towards overcoming these and other problems.
According to the invention there is provided a collapsible filter element for a transcatheter embolic protection device, the filter element comprising:
a collapsible filter body which is movable between a collapsed stored position for movement through a vascular system and an expanded position for extension across a blood vessel such that blood passing through the blood vessel is delivered through the filter element;
a proximal inlet portion of the filter body having one or more inlet openings sized to allow blood and embolic material enter the filter body;
a distal outlet portion of the filter body having a plurality of outlet openings to allow through-passage of blood, but to retain embolic material within the filter body;
the filter body being of an oriented polymeric material.
In one embodiment of the invention the filter element comprises a collapsible support frame, the support frame being movable between a collapsed position for movement through the vascular system and an extended outwardly projecting position to support the filter body in the expanded position. Preferably the filter body is independent of the support frame. Ideally the filter body comprises a membrane.
In one case the filter body has a stored axial orientation in excess of 15%. Preferably the filter body has a stored axial orientation in excess of 20%. Most preferably the filter body has a stored axial orientation in excess of 30%. Ideally the filter body has a stored axial orientation in excess of 40%.
In a preferred embodiment in the material is biaxially oriented.
The filter body may have a stored biaxial orientation in excess of 30%. Preferably the filter body has a stored biaxial orientation in excess of 60%. Most preferably the filter body has a stored biaxial orientation in excess of 80%. Ideally the filter body has a stored biaxial orientation in excess of 100%.
In another embodiment of the invention the ultimate tensile strength of the oriented polymeric material of the filter body is at least 15,000 psi (103.425 MPa). Preferably the ultimate tensile strength is at least 25,000 psi (172.375 MPa). Most preferably the ultimate tensile strength is at least 35,000 psi (241.325 MPa). Ideally the ultimate tensile strength is at least 40,000 psi (275.8 MPa).
The material of the filter body may be of polyester of polyamide. The material of the filter body is preferably of polyester.
In one embodiment the material of the filter body is selected from polyethyleneterephthalate (PET), polybutyleneterephthalate (PBT) and polynapthylterephthalate (PNT). The material of the filter body is preferably of PET.
In another embodiment the material of the filter body is of polyamide.
In one case the material of the filter body is an elastomer. Preferably the material of the filter body is a polyurethane.
In a preferred embodiment of the invention the polymeric material of the filter body is oriented at a temperature below the glass transition temperature of the material.
The material of the filter body may be oriented by stretch blow moulding.
Desirably the filter body comprises a proximal body section, a distal body section and an intermediate body section interconnecting the proximal and distal body sections.
In one embodiment of the invention the frame comprises a plurality of engagement segments, the engagement segments being spaced-apart longitudinally and transversely when the filter is in the deployed expanded configuration to urge the filter body into apposition with the vessel wall. The engagement segments preferably define at least one at least partially substantially helical engagement track.
According to another aspect the invention provides a method for manufacturing a filter body for a transcatheter embolic protection device comprising forming a filter body of oriented polymeric material.
The filter body may be formed by applying an axial stretching force to a hollow body of polymeric material.
The filter body may be formed by applying a circumferential force to a hollow body of polymeric material.
Ideally the method comprises stretch blow moulding a polymeric material.
In one embodiment of the invention the polymeric material is oriented to a temperature above the glass transition temperature of the material or one of its phases, and below the melting temperature of the material.
The method preferably comprises the step of conditioning the formed filter body. Ideally the conditioning is carried out at a temperature in the region of the crystallization temperature of the material.
Desirably the method comprises providing inlet and outlet holes in the body of oriented material. Ideally the holes are provided by
filling the formed body with a filter material;
machining holes in the filled body; and
removing the filler material.
In one case the filler material is a soluble material, such as polyethyleneglycol.